In an image sensor including light receiving elements that are two-dimensionally arrayed at high density, a structure in which a microlens is arranged for each light receiving element is used in order to increase the light-use efficiency, that is, to increase the responsivity. For example, in a light receiving element formed on an InP substrate, a method has been proposed in which the rear surface of the InP substrate is processed into a lens shape to form a monolithic lens (PTL 1). Also disclosed is a method in which thin plate-shaped silicon, germanium, or sapphire is processed to form a microlens array, and the microlens array is then bonded to a light receiving element array (sensor) (PTL 2). In another proposed method, a resin layer functioning as an underlayer of a lens is formed on a sensor, and a microlens composed of a resin is formed on the resin layer so as to form fine irregularities on a surface thereof, thereby suppressing reflection and increasing the light-condensing efficiency (PTL 3).